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Land-atmosphere exchange of carbon in a high-Arctic wet tundra ecosystem

Tagesson, Torbern LU (2011) In Meddelanden från Lunds universitets geografiska institution. Avhandlingar 192.
Abstract (Swedish)
Popular Abstract in Swedish

Under den senaste tiden har problematiken med klimatförändringarna debatterats livligt. För att kunna förutspå den framtida omfattningen av klimatförändringarna och vilka konsekvenser dessa kommer att ha är det ytterst relevant att känna till utbytet av växthusgaser mellan atmosfär och jordens alla ekosystem. Arktiska ekosystem är ytterst känsliga för den globala uppvärmningen. Därtill har temperaturökningen varit större i dessa områden och är förutspådd att bli ännu större i framtiden. Två växthusgaser av extra stor betydelse är koldioxid och metan.

De arktiska ekosystemen spelar dessutom en extra stor roll i kolutbytet mellan mark och atmosfär. Våtmarker på tundran är kalla,... (More)
Popular Abstract in Swedish

Under den senaste tiden har problematiken med klimatförändringarna debatterats livligt. För att kunna förutspå den framtida omfattningen av klimatförändringarna och vilka konsekvenser dessa kommer att ha är det ytterst relevant att känna till utbytet av växthusgaser mellan atmosfär och jordens alla ekosystem. Arktiska ekosystem är ytterst känsliga för den globala uppvärmningen. Därtill har temperaturökningen varit större i dessa områden och är förutspådd att bli ännu större i framtiden. Två växthusgaser av extra stor betydelse är koldioxid och metan.

De arktiska ekosystemen spelar dessutom en extra stor roll i kolutbytet mellan mark och atmosfär. Våtmarker på tundran är kalla, vattenfyllda och syrefattiga, vilket gör att nedbrytningen av dött organiskt material sker långsamt. Eftersom detta pågått sedan den senaste istiden, har stora mängder kol ansamlats i marken i dessa områden. Ca 16 % av jordens yta är täckt av permafrost, men 50% av jordens markbunda kol är lagrad i dessa områden. Dessutom gör dessa förhållandena att en stor del av slutprodukten av nedbrytningen av dött organiskt material är metan. Jag presenterar i denna avhandling studier av utbytet av koldioxid och metan mellan mark och atmosfär i en högarktisk våtmark belägen på Nordöstra Grönland.

Mina studier visade att våtmarken fungerade som en kolkälla under den varma och fuktiga mätperioden 2008. Medan den var en kolsänka under den kallare och torrare mätperioden 2009. Variationen i metanutbytet styrdes av marktempertur, växternas produktivitet, halt av substrat för metanproduktion (organiska syror), vattennivån i marken, samt växternas artsammansättning.

Jag har även undersökt växternas koldioxidupptag mellan 1992 och 2008 genom att kombinera fältmätningar av koldioxid med satellitbilder. Mina resultat visade på en kraftig ökning av koldioxidupptaget under denna tidsperiod. Under samma period skedde även en kraftig ökning av lufttemperaturen, vilket tyder på att det ökade koldioxidupptaget var klimatrelaterat. Jag studerade också metanutbytet mellan 1997 och 2010. Jag fann inga indikationer på förändringar i varken metanutsläpp eller i de faktorer som kraftigast styr metanutsläppen från våtmarken, d.v.s. marktemperatur på 10 cm djup och vattennivå.

Den globala uppvärmningen förutspås att fortgå i framtiden och globala klimatmodellerna förutspår framtida förändringar i såväl temperatur som nederbörd. Resultaten jag presenterar i denna avhandling visar på att dessa förutspådda framtida klimatförändringen kan ha en stark påverkan på kolcykeln i de högarktiskta ekosystemen. (Less)
Abstract
Arctic ecosystems play a key role in the terrestrial carbon (C) cycle, but spa-tially explicit data on the C exchange is scarce in these remote areas. The global warming is especially dominant in the Arctic, and these areas are vul-nerable to climate change. It is therefore important to quantify and understand the processes affecting the C dynamics in these regions. In this thesis, the land-atmosphere exchange of C, with an emphasis on methane (CH4), was measured in a high-Arctic wet tundra ecosystem (Rylekærene) in Zackenberg, north-eastern Greenland.

Rylekærene was a heterogeneous area concerning the source strength of CH4 and concerning which environmental variables that best determine the CH4 fluxes. For the central parts of... (More)
Arctic ecosystems play a key role in the terrestrial carbon (C) cycle, but spa-tially explicit data on the C exchange is scarce in these remote areas. The global warming is especially dominant in the Arctic, and these areas are vul-nerable to climate change. It is therefore important to quantify and understand the processes affecting the C dynamics in these regions. In this thesis, the land-atmosphere exchange of C, with an emphasis on methane (CH4), was measured in a high-Arctic wet tundra ecosystem (Rylekærene) in Zackenberg, north-eastern Greenland.

Rylekærene was a heterogeneous area concerning the source strength of CH4 and concerning which environmental variables that best determine the CH4 fluxes. For the central parts of Rylekærene, temporal variability in CH4 fluxes was well correlated with soil temperature, gross primary production (GPP), active layer thickness and soil organic acids. The spatial variability in CH4 fluxes was closely correlated to water table depth (WtD), species compo-sition and soil organic acids. The CH4 fluxes remained low during autumn and early winter of both 2008 and 2009. The central parts of Rylekærene acted as a C source during the warmer and wetter measurement season of 2008, whereas it was a C sink during the colder and drier measurement season of 2009.

At a site at the edge of Rylekærene, CH4 emissions were lower than at the central parts of the fen, most likely because of lower WtD and different plant species composition. At this site, the variability in CH4 flux was not explained by any of the above-mentioned factors. Increases in CH4 fluxes coinciding with soil freezing after the growing seasons were observed here in 2007, 2009 and 2010.

Changes in peak growing season GPP 1992 to 2008 was investigated by combining satellite data with ground-based GPP measurements. The modeled results show a substantial increase in peak growing season GPP during this period. The GPP increase was accompanied by a strong increase in air tem-perature, possibly indicating that the increase in GPP was climate-driven.

Changes in CH4 fluxes 1997-2010 was studied by combining satellite data with CH4 flux measurements. During 1997-2010, there were no major changes in modelled CH4 fluxes in Rylekærene, and during this period no trend in soil temperature at 10 cm depth and WtD were seen. However, as changes both in temperature and hydrology are expected as global warming continues, it can be assumed that such changes will have strong effects on the land-atmosphere exchange of C in wet tundra ecosystems in the future. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Roulet, Nigel, McGill University
organization
publishing date
type
Thesis
publication status
published
subject
keywords
carbon, methane, carbon dioxide, climate change, Arctic, NDVI, NDWI, micrometeorology, remote sensing, chamber, tundra
in
Meddelanden från Lunds universitets geografiska institution. Avhandlingar
volume
192
pages
33 pages
publisher
Lunds universitets geografiska institution
defense location
Världen, Geocentrum I, Sölvegatan 10, Lund
defense date
2011-03-25 10:00
ISSN
0346-6787
ISBN
978-91-85793-17-4
project
MERGE
language
English
LU publication?
yes
id
5756445a-9bb7-45d7-bca8-0604ed55f449 (old id 1789461)
date added to LUP
2011-03-07 14:58:54
date last changed
2016-09-19 08:44:45
@phdthesis{5756445a-9bb7-45d7-bca8-0604ed55f449,
  abstract     = {Arctic ecosystems play a key role in the terrestrial carbon (C) cycle, but spa-tially explicit data on the C exchange is scarce in these remote areas. The global warming is especially dominant in the Arctic, and these areas are vul-nerable to climate change. It is therefore important to quantify and understand the processes affecting the C dynamics in these regions. In this thesis, the land-atmosphere exchange of C, with an emphasis on methane (CH4), was measured in a high-Arctic wet tundra ecosystem (Rylekærene) in Zackenberg, north-eastern Greenland. <br/><br>
 Rylekærene was a heterogeneous area concerning the source strength of CH4 and concerning which environmental variables that best determine the CH4 fluxes. For the central parts of Rylekærene, temporal variability in CH4 fluxes was well correlated with soil temperature, gross primary production (GPP), active layer thickness and soil organic acids. The spatial variability in CH4 fluxes was closely correlated to water table depth (WtD), species compo-sition and soil organic acids. The CH4 fluxes remained low during autumn and early winter of both 2008 and 2009. The central parts of Rylekærene acted as a C source during the warmer and wetter measurement season of 2008, whereas it was a C sink during the colder and drier measurement season of 2009.<br/><br>
 At a site at the edge of Rylekærene, CH4 emissions were lower than at the central parts of the fen, most likely because of lower WtD and different plant species composition. At this site, the variability in CH4 flux was not explained by any of the above-mentioned factors. Increases in CH4 fluxes coinciding with soil freezing after the growing seasons were observed here in 2007, 2009 and 2010.<br/><br>
 Changes in peak growing season GPP 1992 to 2008 was investigated by combining satellite data with ground-based GPP measurements. The modeled results show a substantial increase in peak growing season GPP during this period. The GPP increase was accompanied by a strong increase in air tem-perature, possibly indicating that the increase in GPP was climate-driven.<br/><br>
 Changes in CH4 fluxes 1997-2010 was studied by combining satellite data with CH4 flux measurements. During 1997-2010, there were no major changes in modelled CH4 fluxes in Rylekærene, and during this period no trend in soil temperature at 10 cm depth and WtD were seen. However, as changes both in temperature and hydrology are expected as global warming continues, it can be assumed that such changes will have strong effects on the land-atmosphere exchange of C in wet tundra ecosystems in the future.},
  author       = {Tagesson, Torbern},
  isbn         = {978-91-85793-17-4},
  issn         = {0346-6787},
  keyword      = {carbon,methane,carbon dioxide,climate change,Arctic,NDVI,NDWI,micrometeorology,remote sensing,chamber,tundra},
  language     = {eng},
  pages        = {33},
  publisher    = {Lunds universitets geografiska institution},
  school       = {Lund University},
  series       = {Meddelanden från Lunds universitets geografiska institution. Avhandlingar},
  title        = {Land-atmosphere exchange of carbon in a high-Arctic wet tundra ecosystem},
  volume       = {192},
  year         = {2011},
}